1. Field of the Invention
The present invention relates to a projection type liquid crystal display apparatus for displaying a large quantity of character information and various other images, and more particularly to a projection liquid crystal display apparatus which projects, onto a screen, light transmitted a plurality of twisted nematic type liquid crystal layers so as to perform a display of enlarged images.
2. Description of the Prior Art
A projection type liquid crystal display apparatus using a plurality of twisted nematic type liquid crystal panels has been developed as a liquid crystal apparatus for displaying a large quantity of character information and/or various images. FIG. 5 is a conventional projection type liquid crystal display apparatus, which has a double-layer liquid crystal display element 6 composed of a pair of laminated liquid crystal panels 60 and 70. Light from a light source 31 enters into a converging lens 32 by which the light is made parallel, and then projected onto the liquid crystal panel 60, in which the light is modulated to a predetermined display pattern transmitted to the other liquid crystal panel 70. The light reaches a screen 35 through a projection lens 34 by which an enlarged image is displayed onto the screen 35.
The liquid crystal panel 60 positioned at the light source 31 side, as shown in FIG. 6, comprises a twisted nematic type liquid crystal layer 61 that is sandwiched between a pair of substrates 62 and 63. The other liquid panel 70 positioned at the screen 35 side comprises a twisted nematic type liquid crystal layer 71 that is sandwiched between a pair of substrates 72 and 73, as well.
The liquid crystal layer 61 at the liquid crystal panel 60 at the light source 31 side is a liquid crystal called an STM (super twisted nematic) or SBE (supertwisted birefringence effect) type of the liquid crystal molecules, that has an angle of twist 180.degree. to 270.degree.. The liquid crystal molecules of the liquid crystal layer 71 of the other liquid crystal panel 70 at the screen 85 side is of the STN (or SBE) type that has a twisting direction that is reverse to that of the liquid crystal molecules of the liquid crystal layer 61 of liquid crystal panel 60. The orientation of the liquid crystal molecules of one of the liquid crystal layers 61 and 71 in the vicinity of the other liquid crystal layer is at an angle of about 90.degree. to that of the liquid crystal molecules of the other liquid crystal layer in the vicinity of the first one liquid crystal layer.
The liquid crystal layer 61 of the liquid crystal panel 60 at the light source 31 side is operated by a multiplex drive. As shown in FIG. 7, a large number of transparent scanning electrodes 64 that extend in parallel to each other are disposed on the substrate 62 that constitutes the liquid crystal panel 60. The respective scanning electrodes 64 being connected to a scanning side drive circuit 66 and being all driven by the drive circuit 66. On the other substrate 63 opposite to the substrate 62 across the liquid crystal layer 61 are disposed a large number of signal electrodes 65 that are positioned so as to be perpendicular to the scanning electrodes 64, respectively. A predetermined voltage is selectively applied to each of the signal electrodes 65 by scanning side drive circuits 67a and 67b.
However, on the contrary, the substrates 72 and 73 at the liquid crystal panel 70 disposed at the screen 35 side are not provided with such electrodes.
With such a liquid crystal display apparatus, a voltage is sequentially selectively applied to each of the scanning electrodes 64 of the liquid crystal panel 60 at the light source 31 side by the scanning side drive circuit 66. A voltage is selectively applied to a predetermined signal electrode 65 on the basis of a display pattern by means of a signal side drive circuit 67a or 67b. The transmitted light is modulated in the portion (a picture element) of the liquid crystal layer 61 corresponding to an intersection of both electrodes to which a voltage has been applied. The light that has been transmitted through the liquid crystal panel 60 is then transmitted through the liquid crystal panel 70 at the screen 35 side. The liquid crystal panel 70 compensates the coloration of light that has been transmitted through the liquid crystal layer 61 of the liquid crystal panel 60, the coloration being caused by the birefringence effect of the liquid crystal layer 61.
A conventional display apparatus with the above-mentioned structure enables the scanning electrodes 64 to scan in 400 lines by, for example, 1/200 duty drive.
It is required that liquid crystal display apparatuses have picture elements with a high density so as to increase the capacity of display. The above-mentioned conventional liquid crystal display apparatus that attains the aforesaid multiplex drive, when the number of the scanning electrodes are increased, so that the picture elements can be highly densified, creates a problem in that a sufficient voltage is not applied to a picture element of the liquid crystal, and the contrast of the resulting display or the response speed is lowered, resulting in a remarkably deteriorated display quality. When non-linear devices, such as diodes, or switching devices such as thin film transistors are added to each of the liquid crystal picture elements, the above-mentioned lowering of the contrast or the response speed can be prevented, but an opening ratio, that is a ratio of the area of the picture elements to the area of the display surface of the liquid crystal layer is lowered, which is considered to be disadvantageous in an economical aspect. Moreover, in a direct visual type liquid crystal display apparatus, different from the above-mentioned projection liquid crystal display apparatus, which comprises a plurality of laminated liquid crystal layers each of which is provided with a voltage applying means, parallax arises in each of the display portions of the laminated liquid crystal layers, which makes it impossible to perform a continuous display, causing the lowering of the quality of the display. Moreover, a conventional projection liquid crystal display apparatus with the above-mentioned electrode disposition (electrode pattern), gaps exist between the electrode (between the picture elements), and accordingly it is difficult to obtain a wide opening ratio when the picture elements are highly densified.